Ensign Ruppenthal served as the pilot of a F4U-4 Corsair fighter with Fighter Squadron 192 aboard the carrier USS Princeton (CV-37). On 21 April 1951, while on a combat mission, his aircraft received a direct hit by anti-aircraft fire and its engine lost oil pressure. It ditched at DU 1303. Helicopter rescue could not locate him. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

For his leadership and valor, Ensign Ruppenthal was awarded the Distinguished Flying Cross, the Air Medal with Gold Star, the Purple Heart, the Combat Action Ribbon, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.